Paper towel and process of producing the same



Patented Feb. 4, 1930 UNITED, STATES enonen a momma, MILTON o.

SCHUR, AND ROYAL H.

RASCH, OF BERLIN, NEW

HAMPSHIRE, ASSIGNORS TO BROWN COMPANY, OF BERLIN, NEW HAMPSHIRE, A

CORPORATION OF MAINE PAPER TOWEL AND PROCESS OF PRODUCING THE SAME No Drawing.

This invention has relation to absorptive paper products, and is more specifically concerned with the manufacture of paper towels.

Among the prime qualities desirable in a papertowel are high absorptive capacity and high wet strength. It is further desirable that treatment to increase the wet strength of they towel should not lower its absorptive capacity. Inasmuch as the wet strength of a towel can be increased only at the sacrifice of its absorptive capacity by thefluse of such sizing material as aluminum resinate, paraflin, oil, rubber, or'the like, it usually contains little, if any, sizing material. Consequently, when wetted with water, it immediately undergoes a material loss in strength. Even a relatively strong towel made from kraft or sulphate pulp, upon vigorous wiping with wet hands tends to undergo tearing or disintegration, because of its low wet strength.

The object of the present invention is to produce a towel having a wet strength materially higher than the strength of the usual non-sized towel, without, however, appreciably affecting its water absorptive capacity. We have found that this object may be attained if the fibers are uniformly treated with material from which cellulose may be regenerated, and the cellulose then regenerated on the fibers. The cellulose may be regenerated in situ on the fibers by precipitation from a solution of a suitable cellulose derivative, e. g., viscose, so that the fibers of the towel are bonded together and encased therein. The ability of regenerated cellulose to'increase the wet strength of the towel, but without substantially affecting its absorptive capacity, may best be explained by the fact that a cellophane sheet made from viscose absorbs water when submerged therein, but does not disintegrate, and loses approximately only of its initial strength upon saturation.

The towel of the present invention may be produced by various methods of procedure. Thus, a waterleaf paper or web, after it has been formed and dried on the paper machine, in one case is passed through a solution of viscose. Preferably, a dilute solution is employed, so that it may readily pass into the Application filed April 28,

pores and interstices of the web. The web may be completely dried or else partially dried by evaporating excess water contained therein, and then passed through a suitable setting bath, e. g., a solution of sodium bisulphate and sulphuric acid, thereby effecting a precipitation of regenerated cellulose on all the fibers of the web. The web may then be washed substantially free of acid, steeped, if desired, in a sulphide-removing bath (e. g., sulphurous acid), again washed, dried, and cut'up into'towels. A towel thus made and containing regenerated cellulose, which encases or covers the fibeis and bonds them 'intimately together, has a materially increased wet strength. The method may be controlled so that about 2% regenerated cellulose is resent in the finished towel, which is ren ered tough and very strong without material effect upon its water absorptivity, as the incorporation of 2% regenerated cellulose does not fill the pores and interstices of the web to a material extent. Of course, the percentage of regenerated cellulose present in the finished towel is subject to variation. In any event, however, the method is carried out so that individualfibers are encased in and bonded together. The method, however, is subject to some variation. Thus, the step of evaporating moisture from the web after its immersion in a viscose solution may be omitted, as the web may be passed into a setting or precipitating bath immediately after such immersion.

Another method of producing cellulose in a towel web may be carried out like the usual beater-sizing process. For instance. viscose is added to the towel-making stock in the beater engine, preferably after it has been beaten and is then uniformly disseminated throughout the stock by the beater engine. Regenerated cellulose may then be precipitated on the stock by the addition of a suitable precipitating agent, e. g., an acid, acid mixture, or acid salt, whereupon the stock may be washed, if desired, prior to formation into a web. The stock is then run-over a papermaking machine, formed into towel material, finished, and cut into towels.

If desired, the viscose may be produced in the web from the web itself, and then precipitated in the web in the form of re nerated cellulose. Thus, the web from t e paper machine is passed through a bath of caustic soda of mercerizing strength, similar to that ordinarily used in viscose reparation. The web is then passed throug squeeze rolls to remove therefrom any excess caustic soda solution and to produce therein the concentration of caustic soda; and cellulose (soda cellulose) desired for conversion into viscose. The fibers of the web maythus acquire only a coating or surfacin of soda cellulose, so that upon assage of t e web through a bath of carbon isulphide or through an atmos phere thereof, viscose is formed on the exterior of the fibers. This procedure also does not materially afiect the absorptivity of the web, as the'pores and interstices therein are reserved in a substantially unobstructed cononly the. surface of the The web is then passed precipitating bath to effeet the precipitation of regenerated cellulose from the viscose, whereu on it is washed free of acid content and fina y dried.

Cellulose may also be regenerated in. the

dition substantiall fibers being afiecte through a setting or towel web from other cellulose derivatives.

" from a cuprammonium cellulose For instance, the web may be passed a solution of cellulose nitrate in a suitable nitrocellulose solvent, e. g., an ether-alcohol mixture. The solvent may then be evaporated from the web, thus leaving a film of cellulose nitrate on the web and on the individual fibers thereof. The cellulose may then be regenerated from the nitrocellulose in situ on the fibers, by passing the web through an aqueous denitrating solution of sodium sulphide, ammonium sulphide, or other suitable denitrating compo d. The denitrated web may then be we ed and dried. This procedure, howeve is less desirable, inasmuch as it calls for the use of organic solvents. The cellulose may further be regenerated solution, rather thanfromviscose. Generally,however, the process may be carried out more expediently and more economically by regeneration from viscose. C

The presence of re enerated cellulose in a towel web, while a vanta eous when mechanical pulp, sulphite pu p, or a mixture thereof is used as a raw material, is particularly advantageous when sulphate or kraft pulp is employed-as the raw material. A kraft or sulphate towel having regenerated cellulose present therein possesses characteristics departing materially from a like untreated towel which undergoes a marked loss in strength when'wetted. A kraft towel containing regenerated cellulose, for instance, does not under 0 disintegration and is torn with relative di%cult even if it is vi orously through ably, the towel is crinkled or otherwise roughened at a suitable point in its manufacture, to. improve its wipin quality.

We are aware o the fact that viscose'has been proposed for useasa size for paper, but it should be noted that the present invention involves the presence of regenerated cellulose in a paper towelwithout an sizing or loading materials, that is, a watereaf paper towel, so as to increase its wet strength while maintaining a high absor not, therefore, claim roadly a paper-having regenerated cellulose incorporated therein.

tive capacity. We do We do not herein claim the subject matter of our application Serial No. 140,676, filed October 9, 1926, whichis directed to .the conditionin of cellulose fiber, and more especially o a high alpha cellulose lwood fiber, for conversion into cellulose derivatives, especially the nitrates, and which involves incorporatmg a cellulose'derivative' into such fiber before effecting the conversation of such fiber into cellulose derivatives.

What we claim is: 1. A'non-waterproofed paper towel, contaming about 2% regenerated cellulose encaising and bonding together the-fibers there- 0 2. As an article of manufacture, a highly absorptlve crinkled paper towel composed of lcraft fiber containing regenerated cellulose imparting sufiicient wet strength to the towel so that it will not disintegrate when wiping i wet hands.

ing improved wet strengt acteristics, which comprises treating an unslzed sheet of kraft paper witha material from which cellulose may be regenerated while maintaining substantially its original absorptivity, regenerating the cellulose in the sheet, and crinkling the sheet. In testimony whereof we have aifixed our signatures.

GEORGE A. RICHTER. MILTON O. SCHUR. ROYAL H. RASCH.

'wiped or rubbed wit wet hands an is very tough, strong, and highly absorbent. Prefer- 

